Cydia - An alternative app store for jailbroken devices.
AppShopper - Mac Apps, Mac App Store, iPad, iPhone and iPod touch app store listings, news, and price drops
Zestia - Zestia is a mobile app designed to assist you in organizing your hectic schedule, social life, and professional persona.
AppAgg - Application Aggregator
JazzMyApp - Let JazzMyApp surprise you with amazing apps everyday. Try it out yourself.
AlternativeTo - AlternativeTo lets you find apps and software for Windows, Mac, Linux, iPhone, iPad, Android, Android Tablets, Web Apps, Online, Windows Tablets and more by recommending alternatives to apps you already know.